Controllable chest compressing device

Abstract

 The invention relates a chest compressing device, comprising a power source, a compressing element connected to the power source and a controller, characterised in that it comprises: an electric motor connected to the power source, the controller and the compressing element, and that the controller controls the motor so as to make the compressing element apply compressions with desired/pre-defined characteristics. The invention relates also to a method for controlling CPR.

Description

[0001] The present invention is related to a controllable chest compression device, comprising a power source, a compressing element connected to the power source and a controller. The invention is characterized in that it comprises an electric motor for transferring energy from the power source to the compression element and that the controller controls the motor so as to make the compressing element apply compressions with desired and/or predefined characteristics.

[0002] Sudden cardiac arrest is a leading cause of death in developed countries in the Western World, like United States and Canada. To increase the chance for survival from cardiac arrest, important aspects are CPR (Cardio Pulmonary Resuscitation) and heart defibrillation given in the first few critical minutes after the incident. CPR is performed to ensure a sufficient flow of oxygenated blood to vital organs by external compression of the chest combined with rescue breathing: Heart defibrillation is performed to reestablish normal heart rhythm by delivery of external electric shock.

[0003] The quality of CPR is essential for survival. Chest compressions must be given with a minimum of interruptions, and be of sufficient depth and rate. Manually performed chest compressions represent an extremely exhausting task, and it is practically impossible to give sufficient quality manual CPR during transportation of a patient.

[0004] Many different types of automatic chest compression devices have been developed to overcome this, based on a wide variety of technical solutions.

[0005] US 2006/0094991 describes a method to control the delivery of CPR to a patient through a mechanical CPR device. The method generally allows for a gradual increase of the frequency of CPR cycles. This gradual increase can be regulated by protocols programmed within the CPR device such as intermittently starting and stopping the delivery of CPR, stepping up the CPR frequency, increasing the force of CPR, and adjusting the ratio of compression and decompression in a CPR cycle. The CPR device described in this publication includes a controller with a linked input device. Said controller is linked to the device through the valve. In operation the pump provides a force through the valve and into the compression applying element thereby deforming the element and compression the chest.

[0006] Devices based on tensioning a belt embracing the chest could also have a rotating motor with a spindle being engaged and disengaged. US 6066106 describes a system for performing chest compression in CPR. The system includes a motor and a gearbox including a system of clutches and brakes which allow for controlling and limiting the movement of the compression mechanism and includes a control system for controlling the operation and interaction of the various components to provide for optimal automatic operation of the system.

[0007] Chest compressions given by automatic devices have the potential to be more forceful than manual compressions. There is a balance between 1) giving optimal blood flow to vital organs and 2) limiting the impact to the chest, to avoid internal injuries as a result of the external force being applied to the patient. Previously known automatic chest compression devices are designed mainly with respect to 1), and in many cases do not provide a satisfactory balance between 1) and 2).

[0008] It is an object of the invention to provide control of the compressions with respect to e.g. compression depth, compression frequency, time of compression, time of maintaining a compression, delay time between compressions, rate of relieving and applying pressure, etc. This may be performed by controlling the waveform of the compressions.

[0009] By having control of the compression waveform as applied to the patient, it is possible to achieve an optimal balance for each patient/recipient and for each stage in the treatment. In this way the pulse pattern of the compression/decompression can be adapted to the individual patient at the different stages in the treatment, thus leading to improved therapy concerning both optimized blood flow and avoidance of internal injuries.

[0010] In the context of the present application, the expression "pulse pattern" is used for the signals controlling the motor and for the compressions performed on the patient. These two types of pulse pattern are not necessarily identical but they are related to one another by the characteristics of the motor, of the compressing member and of the transmission mechanism if present.

[0011] The invention comprises as mentioned above a chest compression device which permits control of the compression characteristics. The chest compressing device according to the invention comprises a power source, a compressing element connected to the power source and a controller. The device comprises also an electric motor connected to the power source, the controller and the compressing element. The controller in the device according to the invention controls the motor so as to make the compressing element apply compressions with desired/pre-defined characteristics.

[0012] The invention is characterised by the features mentioned in the patent claims.

[0013] The power source may be any suitable power source for electric power. The compressing element is the interface between the motor and the recipient, and may be a piston with fasteners fastening means (e.g. suction means, adhesive, etc.,) such as a cupping glass, or a device arranged for placement on the patient's chest without fastening to the chest. The compression device can also be a belt or another device for placement round the patient's chest.

[0014] The power source provides the necessary power to the compressing element for applying compressions to the chest of the recipient. Compressions are generated by means of an electric motor. The controller controls the pulse pattern of the compressions/decompressions by controlling the motor. The pulse pattern may be a pre-defined pattern or an adaptive pattern. The pattern can be constant or may be varied dynamically during the compressions, for example based on feed-back from sensors placed on the patient. Such sensors may also be used for choosing a constant pattern from a storage device connected to the controller, to obtain an advantageous pattern for each patient. The sensors may measure any relevant characteristics of the patient, such as electrocardiogram, blood pressure, oxygen content of the blood, etc, or relevant features regarding the CPR, such as compression depth, compression force, compression rate, etc.

[0015] In one embodiment of the invention the motor is a variable speed motor. In another embodiment it has two opposite directions of rotation. In another embodiment the motor is adapted for operation with stationary periods that is, periods with a velocity of 0 RPM. The motor can be a low inertia servo motor. In another embodiment of the invention the motor is a brushless motor. The motor can e.g. handle an average power higher than 100W; it can have a kinetic energy lower than 4J at top speed in operation and a weight lower that 500 grams. It is also possible for the motor to have only one of these features or any combination of two of these features

[0016] Although different features of the invention are described as belonging to different embodiments, it is fully possible to combine these in a single embodiment, as e.g. having a low inertia, brushless servo motor.

[0017] In one embodiment the invention comprises a transmission mechanism for transmission of mechanical energy from the motor to the compressing element. This mechanism can comprise pneumatic means, it can comprise mechanical means or it can comprise a combination of pneumatic and mechanical means.

[0018] The power source can comprise at least one high power lithium ion battery or any other battery adapted to supply energy directly to the motor. It can also comprise at least one battery indirectly connected to the motor. The power source can be adapted for connection to AC or DC mains.

[0019] The device according to the invention is in one embodiment adapted to permit free return of the compressing element to an upper position.

[0020] To achieve a satisfactory quality for chest compressions (frequency, speed and force) the motor must be able to accelerate very swiftly and at the same time must be able to provide high power in short periods of time. These requirements are fulfilled by servo motors with low rotational inertia, and which are adapted for high peak power.

[0021] Use of an electric motor with a controller permits full control of the compressions with respect to most or all of the important issues, such as compression depth, compression force, compression frequency, duration of compressions, rate of relieving and applying pressure, etc. This may be performed by controlling the waveform/pulse pattern of the compressions.

[0022] In one simplest embodiment, the pulse pattern may be one constant pattern comprised in a storage device for use on all patients. However it may be possible to update the stored pulse pattern, for example when the international guidelines are changed or when research results points on better pulse patterns. Such updates may be performed by replacing the storage device with an updated storage device, by connecting to an external computer, etc.

[0023] The storage device may be connected to the controller and may, in addition to or instead of pre-defined pulse pattern(s), comprise algorithm for generating an optimal pulse pattern, for example based on sensor signals.

[0024] The controller in one embodiment of the invention permits to extract and log chest compression data. This gives a unique possibility for clinical studies and optimization of the system. Internal injuries could be related to for instance the depth profile of the compression piston, etc. Logging data would enable research into this topic and others.

[0025] The invention will now be described by means of examples illustrated in the drawings, where:

fig. 1 a shows a "traditional" pulse pattern for chest compressions as used by prior art automatic chest compression devices;

fig. 1b shows an example of a possible improved pulse pattern;

figure 2 is a block diagram of an embodiment of the chest compression device according to the invention,

figure 3 is a more detailed block diagram of an embodiment of the device according to the invention,

figure 4 is a more detailed block diagram of an embodiment of the device according to the invention,

figure 5 shows an example of compression depth and motor velocity vs. time.

[0026] Figure 1a shows a pulse pattern (compression depth vs. time) which corresponds to prior art automatic chest compression devices. Here the compressions 10/decompressions 11 are performed with similar quick velocity/during a short period of time. This implies the necessary compression force to be directed onto the patient during the same short period of time, and the compressions have therefore a violent impact to the patient. The time 12 between compression and decompression and the time 13 between decompression and compression has the same order of magnitude.

[0027] The curve in figure 1b shows a modified pulse pattern which provides controlled compression 15, e.g. longer compression time/slower rate, and thus more limited patient impact, combined with a quick decompression 16. The time 14 between compression and decompression and the time 17 between decompression and compression can be equal or different and have the same or different orders of magnitude.

[0028] This is an example of a pulse pattern which can be achieved by means of the invention. The process will be more gentle to the patient, with reduced risk for injuries. Other pulse patterns may be applied with other properties, for example according to what is assumed to be optimal for the patient, according to new knowledge and/or guidelines within the art. Such patterns may for example have different delays between compression/decompression and decompression/compression, or other curvatures of the compressions/decompressions.

[0029] Figure 2 is a block diagram of an embodiment of a chest compression device according to the invention. The aim of the device is to apply chest compressions on a patient in a controlled manner. The device comprises a servo motor 21 connected to a transmission mechanism 22 for transforming rotation movement in the motor 21 into a reciprocating movement. The transmission mechanism 22 is connected to a compression element 33, which can e.g. be formed as a plate, a vacuum cup or a round shaped body. The compression element 23 is driven by the motor 21 to perform compressions. The device comprises also a servo controller 24 which among other functions is in charge of controlling the motor's operating cycle. The servo controller 24 is adapted to drive the motor 21 with any digital modulated pulse pattern. As shown in the figure, there may be provided feedback signals 26 from the patient 25 to the servo controller 24. It is also possible to provide control signals 27 related to the transmission mechanism 22 as feedback for motor control. The device also comprises a power source 28.

[0030] As mentioned before, in one embodiment of the invention motor 21 fulfills certain requirements regarding: a) kinetic energy at max speed, b) peak power, c) efficiency (at a given power), d) weight and dimensions.

[0031] Limited kinetic energy provides dynamic performance that is, the ability to freely select a displacement profile for the compression element without high power consumption. Limited kinetic energy also provides safety as if there is a fault in the electrical power system causing all the kinetic energy to be released into the patient's chest. This sets a limit for the kinetic energy of about 4J (breast stiffness 200N x displacement 0.02m = 4J).

[0032] Peak power, with for example a maximum force of 550N transferred to a patient and a maximum retraction speed for the compressing element of 0,63m/s is: P= 550N x 0.63 m/s = 347W. This is the power necessary at the patient's end, and losses in the transmission mechanism must be taken into consideration. This leads to a peak power for the motor in one embodiment of the invention of 400W-600W.

[0033] In one embodiment of the invention, it permits substantially free return of the patient's chest to a non-compressed position by retracting the compressing element at high speed (e.g. 0,63m/s). In another embodiment a substantially free return of the chest to an uncompressed position is permitted by means of the transmission mechanism (e.g. by mechanically disconnecting the motor from the compression element). In this case the maximum return speed requirement will not be decisive and a motor with a peak power of e.g. 300W-500W can be used.

[0034] High efficiency has as a consequence to long battery life and little generation of heat. Motor 1 has in one embodiment of the invention efficiency of around 75%, but motors with other efficiencies can also be used.

[0035] Weight and dimensions are limited in an embodiment of the device adapted for portable use. In said embodiment the motor's weight is limited to 500 grams.

[0036] Other parameters of importance can be average power (to avoid overheating a motor in one embodiment of the invention has an average power higher than 100W), voltage (insulation strength), motor constants (rpm/V, etc), durability, radial and axial load on bearing.

[0037] Motor 21 can e.g. be a brushless DC motor (e.g. a motor with a peak power equal or higher than 400 W and efficiency higher than 75%, or e.g. a motor with a peak rating up to 500 W and 150 W average rating, as e.g. a brushless Minebae 40S40A) or it can be a DC motor with brushes. If transistors provide the commutation, any variant or combination of block commutation or sinus commutation might be used. Motor 1 can comprise a controller structure with feed forward.

[0038] Figure 3 shows a more detailed block diagram of the device according to the invention. This diagram shows controller 24 comprising 3 elements: a motor controller 31, a main controller 32, user controls and data logging 33. This division is done purely for illustration purposes as the three elements can be integrated in a single device, or any two elements can be integrated while one element is provided separately. Motor controller 31 has as a function to sense the motor rotational position and to control operation of the motor and also the motor's connection to the battery 30. Main controller 32 can receive signals from different sensors and provide feedback signals to control the device. Main controller 32 is also able to receive signals not generated by the device itself, as e.g. user controls, patient feedback data and output values of signals providing data logging.

[0039] Figure 4 is a more detailed block diagram of one embodiment of the device according to the invention.

[0040] This embodiment of the device comprises a power source equipped with battery 30 for providing power to motor 21 via a three phase bridge 41. Battery 30 has in one embodiment of the invention (shown in figure 4) a capacity of 2,3 Ah, it is able to deliver more than 600W of peak effect and it has an inner resistance lower than 0,3Ω. In portable versions of the device, the battery has a weight of less than 1 kg and a volume of approximately 200mmx80mmx80mm. The battery must not overheat when it delivers an average power of 150W at an ambient temperature of 40 degrees Celsius. These requirements are met e.g. by high power lithium ion cells as ANR26650MI available from A123 Systems Inc or by other batteries capable of delivering energy directly to the motor (that is, without intermediate energy storage).

[0041] Intermediate storage of energy will be provided in the embodiments of the device which comprise batteries not complying with the above mentioned requirements, energy storage in capacitors might help with the 600W peak power requirement. If a boost circuitry is used to achieve a constant battery current during the compression cycle, the battery heat dissipation can be limited and batteries with less power handling capability than the A123 system can be used.

[0042] Another possibility (not shown) is to provide a power source adapted for connection to AC or DC mains with a small 100W power supply if the high power lithium ion battery (or batteries) is connected in parallel with the supply. The battery will provide the peak power needed for the device operation while the power supply will ensure that the battery does not discharge. Using batteries in stead of capacitors for energy storage will ensure that the device operation is not interrupted if the power supply is disconnected for a short period when moving the patient from one room to another etc. In one embodiment of this invention capacitors are used in stead of batteries.

[0043] A combination of the above mentioned embodiments is also possible.

[0044] Motor power control circuit 40 is activated in case of an error situation. The circuit will cut the supply to the motor e.g. by opening the battery high side connection to the bridge circuitry. The motor power control 40 can be activated by: a) a motor controller circuit 25, b) manually (emergency stop 22), c) the main controller 12, d) a low battery voltage signal, e) low/high regulated 5V and 3,3V (not shown), d) hardware shutdown as a consequence of high peak current. If the motor controller 45 fails and the bridge current rises, the main controller 32 can initiate a shut down. A hardware solution can be available if faster shutdown is needed. Some embodiments of the invention can comprise only one or a selected group of the above mentioned activating inputs. Substantially all input lines to motor power control 40 have to be activated in order for the switch to turn "on" and allow compressions of the patient.

[0045] As mentioned above battery 30 delivers power to motor 21 via motor power controller 40 and three phase bridge 41. The bridge circuit 41 can have an energy storage capacitor (not shown) which might aid compression element return in an error mode. Bridge 41 comprises high side transistors (not shown) which can run at 100% duty cycle in order to achieve block commutation of the motor 1. In an embodiment of the invention battery voltage is limited to 30V and the bridge can comprise mosfets with breakdown voltage 60V.

[0046] The motor controller circuit 45 drives the motor in accordance with a drive profile that is, a determined sequence of digitally modulated pulses with a determined shape. Circuit 25 will encompass all the necessary drive algorithms needed.

[0047] Figure 4 shows many inputs to controller 45, and some of these can be omitted. Inputs: a) Hall elements 48 for indication of the position of the motor rotor and thus the compression element's position, b) Two absolute positions corresponding to monitoring of the position of the compression element with two limits: a bottom position (full compression) and a high position (no compression). The position limit interval at the bottom shall be regarded as absolute stop position; movement beyond this position shall be minimal. The top position can be used for resetting a Hall sensor signal count. Counting Hall sensor pulses from this position will provide information relating to the piston position. A middle position is used for checking the mechanic movement during operation, c) Force (49) analogue input, d) motor current monitoring, e) battery output current and voltage monitoring, f) Input power from regulator, g) Input from main controller 12, activating compression element movement, h) Input from motor power control circuitry 20, i) motor temperature measurement.

[0048] Outputs: a) Power off signal to motor power control 40, b) outputs for test and verification, c) Bridge gate signals for mosfets 41, d) Charge pump switch signal to enable the drive voltage for the top mosfets (not shown), e)Signals to the alarm circuits.

[0049] The motor controller in this embodiment of the invention comprises software for performing the following tasks: 1) Communication and control between the main controller 32 and the motor controller 45, the main controller can download a "drive profile" to the motor controller 45 prior to activation of device movement. The drive profile encompasses desired depth waveforms with respect to time and force limitations (see e.g. figure 1a); 2) Communication encompasses also all relevant status/measurement data obtained by the motor controller 45. The communication protocol is designed to detect deviations from normal functionality, 3). The software identifies erroneous movement or lack of movement of the device, overheating, and deactivates the motor power control 40 in order to safeguard the "patient". The software must also respond to overheating of the motor and the drive electronics, 4) Both processors 32 and 45 can shut down the system, and initiate alarms.

[0050] Motor controller 45 is in charge of controlling operation of motor 21 by controlling operation of the three phase bridge 41. As a safety measure, the device can be adapted to proceed in such a way that if battery 30 is suddenly removed the main controller 32 notices the removal and immediately initiates a controlled shut down.

[0051] Safe termination of operation can be limited to turning off bridge 41 thus allowing the compression element 23 (figures 2 and 3) to return using the chest force to push the piston to the top position. In an alternative embodiment a controlled return to high compression element position is needed.

[0052] During start up the main processor 32 will control all the device's parts. When the system is "good to go" a signal will be given to the motor controller 45. The software comprises drive algorithms in order to safely drive the motor/device in the various states of operation, which include: A) Start position: the compression element is kept close to the upper compression position when mounting the machine on the patient, B) Upper compression position: The compression element can be kept in position by the force from the patient chest, C) Movement down according to depth profile, D) Limitation of force, movement regulated to maximum force, E) Hold at accurate depth, F) Return to Upper position. The above mentioned steps are partly illustrated in figure 5.

[0053] Figure 5 shows two curves. The upper curve shows the inverted compression depth vs. time, where the value of compression depth is multiplied by 0,125 (400=50mm). The lower curve shows the motor RPM, where the maximum speed at compression is limited to 3500 RPM in order to avoid chest injuries while the decompression is done at high speed (-5000 RPM) in order to maximize the patient blood flow. As one can see from the lower curve, the motor is accelerated at the beginning of a compression cycle and thereafter it experiences a reduction in velocity until the lowest compression point is reached. After a short interval with constant speed (maximum compression), a high acceleration period follows to allow the chest to decompress naturally. The waveform shown in this figure is only meant for illustrative purposes as the invention permits use of any waveform in the compression process.

[0054] As one can see the device according to the invention permits performance of controlled, swift and effective CPR. The use of an electric motor permits also easy adaption of the compression parameters to different patients and different situations. The electric motor permits regulation of all the necessary parameters in the waveform of the performed compression in a swift manner.

Claims

1. Chest compressing device, comprising a power source, a compressing element connected to the power source and a controller,
characterised i n that it comprises:

an electric motor connected to the power source, the controller and the compressing element, and that

the controller controls the motor so as to make the compressing element apply compressions with desired/pre-defined characteristics.

2. Device according to claim 1, characterised in that the controller is arranged to control the pulse pattern of the compressions/decompressions.

3. Chest compressing device according to claim 1,
characterised in that the motor is a variable speed motor.

4. Chest compressing device according to claim 1,
characterised in that the motor has two opposite directions of rotation.

5. Chest compressing device according to claim 1,
characterised in that the motor is adapted for operation with stationary periods, that is periods with a velocity of 0 RPM.

6. Chest compressing device according to claim 1,
characterised in that the motor is a low inertia servo motor.

7. Chest compressing device according to claim 1,
characterised in that the motor is a brushless motor.

8. Chest compressing device according to claim 1,
characterised in that it comprises a transmission mechanism for transmission of mechanical energy from the motor to the compressing element.

9. Chest compressing device according to claim 1,
characterised in that the power source comprises at least one high power lithium ion battery or any other battery adapted to supply energy directly to the motor.

10. Chest compressing device according to claim 1,
characterised in that the power source comprises at least one battery indirectly connected to the motor.

11. Chest compressing device according to claim 1,
characterised in that the power source is adapted for connection to AC or DC mains.

12. Chest compressing device according to claim 1,
characterised in that the motor can handle an average power higher than 100W.

13. Chest compressing device according to claim 1,
characterised in that the motor has a kinetic energy lower than 4J at top speed in operation.

14. Chest compressing device according to claim 1,
characterised in that the motor has a weight lower that 500 grams.

15. Device according to claim 1,
characterised in that it is adapted to permit free return of the compressing element to an upper position.

16. Device according to claim 2, characterised in that the pulse pattern can be adapted to each patient.

17. Device according to claim 1, characterised in that the controller is programmable.

18. Device according to claim 1, characterised in that it comprises a storage device for storing pulse patterns.

19. Device according to claim 1, characterised in that it comprises sensors for measuring characteristics of the patient, such as electrocardiogram, blood pressure, oxygen content of the blood, etc.

20. Device according to claim 1, characterised in that it comprises sensors for measuring features regarding CPR, such as compressing depth, compressing force, compressing rate, etc.

21. Method for controlling chest compressions performed by a device according to any of the preceding claims,
characterised in that it comprises controlling the characteristics of the compressions.

22. Method according to claim 21,
characterised in that it comprises controlling the motor in such a way that the force is applied with a desired/pre-defined pulse pattern.

23. Method according to claim 22, characterised in that the pulse pattern may be adapted to each patient.

Drawing